Generally, a coating agent is required to form a film capable of preventing the deterioration of the surface of a substrate, is required. Particularly, in recent years, a coating agent which can forma film having chemical resistance at a level of preventing the deterioration of a substrate due to the adhesion of a chemical, such as a detergent, or acid rain, besides warm water resistance or solvent resistance, has been required by the industries.
The coating agent having the above characteristics is often required for protecting the surface of a plastic substrate which is easily deteriorated due to the adhesion of a chemical or the like, or a metal substrate which is easily rusted.
As the coating agent that can be used in protecting the surface of the plastic substrate, for example, there is known an aqueous curable polymer dispersion which contains a polymer particle, a polyfunctional epoxy compound, and a water-based medium, the polymer particle being composed of at least two layers where the A phase of the layers is composed of a carboxyl group-containing polymer and the B phase of the layers is an ethylenic polymer having a basic nitrogen atom-containing group (for example, refer to PTL 1).
However, a film formed using the aqueous curable polymer dispersion fell one step short in terms of warm water resistance, corrosion resistance, and chemical resistance for the purpose of preventing the deterioration of a plastic substrate or a metal substrate over a long period of time. In particular, there was a case that the film is not practically sufficient for preventing the generation of rust from the metal substrate.
Meanwhile, in recent years, an aqueous coating agent in which a resin is dispersed in an aqueous medium has been widely used in various fields for the purpose of achieving the reduction of environmental loads.
As the aqueous coating agent, those containing various emulsifiers in order to impart excellent storage stability and compounding stability are known.
However, there was a case where storage stability or the like cannot be improved depending on the kind of a resin contained in the aqueous coating agent, whether a hydrophilic group exists, and the kind of the hydrophilic group, even when the emulsifier is used. Further, there was a problem that, when the emulsifier is used, the storage stability or the like of the aqueous coating agent is improved, but the adhesiveness of the film to a substrate, warm water resistance, corrosion resistance, chemical resistance, and the like are deteriorated.
Accordingly, an aqueous coating agent excellent in the adhesiveness of the film to a substrate, warm water resistance, corrosion resistance, and chemical resistance has been required.